German Patent No. 38 23 574 describes a drive unit of the type identified above. Within this drive unit, a power contactor is connected upstream from each of two reversing switches which switch without current and the contacts of the power contactor control the switching operations that are subject to load currents. The reversing switches which are not current carrying are provided here as circuit board components, whereas the power contactors with the contacts are not mounted on circuit boards because of their compactness but instead are mounted in a separate space, e.g., in centrally arranged switch boxes. The necessary electric connections between the current-carrying contacts of the power contactor and the non-current-carrying contacts of the reversing switches are created in a conventional way within the switchgear through appropriate cable harnesses for the individual installation.
Depending on the type and extent of the switchgear having a plurality of disconnecting switches and grounding switches which are also equipped with a plurality of motor drives accordingly, there is a variety of different types of cable installations which must also be brought to the various wiring levels through multiple changes because of the differences in current-carrying capacity of the respective power contactors and reversing switches.